The present invention relates in general to a method for growing a monocrystalline gadolinium gallium compound, and more particularly, to a method of maintaining an adherent meniscus between the melt and growing crystal in the process of growing monocrystalline gadolinium gallium garnet.
Semiconductor devices, such as bubble memories, commonly employ crystals of various chemical elements and compounds, wherein gadolinium and gallium compounds are particularly important for use in such devices. It has been found that in order to obtain gadolinium and gallium containing devices having reproducible properties, satisfactory reliability and reasonably satisfactory electrical characteristics, the materials used should preferably be of a high degree of purity. It has further been found that for most applications in order to obtain bubble memories of high quality, the gadolinium and gallium compounds should be obtained from a single crystal of material, that is, material with no intercrystalline boundaries present. This is because a single crystal of a substance will contain fewer impurities than multicrystalline materials; with the latter, there is a greater opportunity for unwanted impurities to become lodged between irregularly small crystal grains than to become crystallized as part of a single crystal.
A method used for preparing single crystals is known as Czochralski's technique. In this method, frequently referred to as the crystal-pulling technique, a seed crystal is dipped into a molten mass of material, and the surface of solidification of the crystal is gradually advanced for the seed crystal to the molten substance. It is apparent that in growing single crystals using such a method, lowering the crucible with the seed affixed is equivalent to raising the seed holder with the crucible maintained in place.
Where the crystal-pulling technique has been used for the growing of monocrystalline gadolinium gallium garnet, it has been found that obtaining uniform crystal growth is adventurous and haphazard. In order for the Czochralski technique to work successfully, the growing crystal must support a column of liquid (meniscus) above the level of the surrounding melt. This meniscus column is held up by the surface tension between the liquid and the growing crystal. It is a well-established phenomenon of physical chemistry that impurities lower the surface tension of liquids. It has been observed frequently in the growth of monocrystalline gadolinium gallium garnet that the meniscus will drop off the crystal due to a low surface tension. When this occurs, crystal growth is effectively prohibited since the essential adhesion between the growing crystal and liquid phase cannot be maintained.
It is therefore an object of the present invention to provide a method for the growth of monocrystalline gadolinium/gallium compounds having effective uniform crystal growth.
It is yet a further object of the present invention to provide a method of maintaining an adherent meniscus between the liquid phase and growing crystal in the process of growing a monocrystalline gadolinium/gallium compound.
It is still a further object of the present invention to provide an improved method for the growth of monocrystalline gadolinium gallium garnet for use in bubble memory applications.
It is yet still a further object of the present invention to provide a chemical method for counteracting the effect of impurities in gadolinium sesquioxide during the crystal growth of gadolinium gallium garnet.